1. Field of the Invention
The present invention relates to a wireless communication system, more particularly, to a receiver and a chipset for dedicated short range communication (DSRC).
2. Description of the Related Art
DSRC is dedicated short range communication. The DSRC denotes a communication manner and protocol that performs local communication without long distance interference based on an industrial/scientific/medical (ISM) band and several frequency bands. The DSRC instantaneously exchanges a large quantity of information within a distance of several to several tens of meters through bilateral wireless communication. Because the DSRC is used in a narrow zone, reuse of a frequency is possible in each zone.
In recent years, the DSRC has been widely used in the Intelligent Transportation System (ITS). An Electronic Toll Collecting System (ETCS) has been greatly highlighted as an example of the ITS. Besides, the DSRC may be used in various fields such as parking management, distribution management, oil station fee payment, or vehicle shopping.
Such a DSRC has been significantly expanding data communication between vehicle-to-vehicle or vehicle-to-infrastructure all over the world. In particular, commercial services using a 5.8 GHz carrier wave are starting to be applied to ETCS and ITS in Asian countries including Korea and Japan. Currently, base equipment installation for ETCS is substantially completed in a national expressway network of Korea. In some cities, traffic information services are provided to ordinary persons using an ITS network.
The following is a description of a protocol of DSRC in Korea.
(a) Assignment of wireless transmission carrier wave: 5800+k×10 MHz (necessity: k=0, 1, selectivity: k=4, 5)
(b) Modulation/demodulation: ASK (Amplitude Shift Keying), modulation index is equal to or greater than 75%
(c) Switching method between transmission/reception modes: Time Division Duplexing (TDD)
(d) Multiplexing technology: Frequency Division Multiplexing (FDM)+Space Division Multiplexing (SDM)
(e) Reception sensitivity range: −76 dBm (for ITS)˜−40 dBm (for ETCS)
(f) Transmission output power: +10 dBm
(g) Moving speed support of On-Board Equipment (OBE): higher than 160 km/h
(h) Temperature variation range of OBE: −85□˜40□
The reception sensitivity range among the foregoing protocols is described. In a national DSRC protocol, it is required that the reception sensitivity is −76 dBm for ITS and the reception sensitivity is −40 dBm for ETCS. The reception sensitivity means a minimal signal input level that a receiver may operate according to characteristics or a performance of a receiver device. The reception sensitivity is determined based on a bit error rate (BER), which is an important factor for discriminating a performance of the receiver.
It is understood that there is a need for very rapid switching time between transmission/reception modes with excellent BER in order to perform a normal billing while an OBE is also moving a narrow ETCS zone at high speed. As a part of multiplexing technology, the use of an SDM means that an undesirable interference signal may be generated from an adjacent ETCS cell. Accordingly, so as to prevent this, there is a demand for the delicate control of transmission and received powers within a wide temperature variation.
A free sensitivity control function of a wide area in a design specification of the OBE in the DSRC is an essential factor simultaneously enabling the support of ITS and ETCS. Further, in order to clearly define a communication area within a wide temperature variation range, a very delicate set of the sensitivity is required together with exact transmission power. In particular, since it is checked by an intensity of received power whether or not the OBE enters within the communication area, there is a need for more exact control of the sensitivity in the ETCS. The reason is that when the sensitivity is less than a predetermined value, the OBE attempts to communicate with a base station prior to entering the communication area to occur interference with an adjacent DSRC device. When the sensitivity is greater than the predetermined value, the communication may be performed in only a narrower area than a defined communication area to reduce available communication time.
As a conventional control method of sensitivity, there has been used a method for controlling a gain of a receiver. Namely, when controlling the gain of the receiver, a noise figure of the receiver varies. By using such a feature, a maximum reception distance satisfying a BER of the receiver is adjusted.
FIG. 2 is a graph illustrating received power PIN versus BER characteristics in a conventional method for controlling the sensitivity of a receiver. In the graph of FIG. 2, an x axis is an intensity of a received signal, namely received power, and a y axis is a BER of the receiver upon reception of a signal having a corresponding intensity. A graph 201 is received signal intensity versus BER graph in a case where a noise figure of the receiver is NF1. A graph 202 is received signal intensity versus BER graph in a case where the noise figure of the receiver is NF2. In this case, NF1<NF2 is satisfied.
When it is required that the receiver operates where the intensity of the received signal is greater than PSEN.1, and that the BER becomes less than 10−5 in an operation range, namely, when there is a need that the sensitivity of the receiver is PSEN.1, the noise figure of the receiver should be set to NF1. In the same manner, when it is required that the receiver operates where the intensity of the received signal is equal to or greater than PSEN.2, and that the BER becomes less than 10−5 in an operation range, namely, namely, when there is a need that the sensitivity of the receiver is PSEN.2, the noise figure of the receiver should be set to NF2. That is, the noise figure of the receiver is changed according to the required sensitivity.
However, disadvantages of such a control method are as follows. Because a system noise figure of the receiver is determined as a function of gains and noise figures of all the structural circuits, it is significantly difficult to linearly control a noise figure of a specific circuit by controlling a gain or the noise figure of the specific circuit. Moreover, since the BER obtained with a maximum system performance index in a minimum input power, is obtained by artificially degrading a performance of a system when the sensitivity is set to a great value, a system of an optimal performance may be not obtained, and it is difficult to define a clear communication distance.
Meanwhile, since a conventional base station for DSRC is configured by a hybrid module configuration of high manufacturing cost and cost burden, it is implemented in a number of construction chips and external components. Accordingly, when specific design matters are changed in the base station of DSRC, the whole quantity of the base station is returned to a laboratory, so that it should be again adjusted. This causes the occurrence of a cost burden. The base station for DSRC implemented in a hybrid module configuration has a disadvantage that it may not be integrated with chips such as GPS or DMB.
Meanwhile, the conventional ASK receiver (not shown) for DSRC reception includes a low noise amplifier (LNA), a mixer, an intermediate frequency (IF) filter, an RSSI, a data comparator, and a frequency synthesizer. The IF filter is positioned in an outside of an ASK receiver chipset. In contrast to this, remaining structural elements are all positioned in an inside of the ASK receiver chipset. The reason why is that since an IF frequency of the conventional ASK receiver for DSRC reception is a high frequency of approximately 40 MHz, a surface acoustic wave (SAW) is used as the IF filter, and since a size of a filter processing a high IF frequency is large, the IF filter may not be integrated in the ASK receiver chipset.
In the ASK receiver for DSRC reception having a high IF frequency, since the IF filter is positioned in an outside of the ASK receiver chipset, it is difficult to match the ASK receiver chipset and the IF filter with each other. Moreover, a size of the ASK receiver is increased, thereby increasing a cost.